One of the great mysteries in science has been understanding how certain species on the planet are able to travel vast distances every year to feeding grounds or to reproduce. Examples abound including migratory birds, fish, whales, turtles, crabs, dinosaurs and carrier pigeons. It has long been known that animals could navigate using the Earth’s magnetic field. In 1963, German zoologist Wolfgang Wiltschko discovered that migratory birds orientated themselves this way. Yet for decades scientists have been at a loss to explain exactly where and how the “compass” works in these creatures.

Now an answer has been found. And the answer is simple. Magnetism within the brain.

The Local Germany reports that a group of Munich scientists have located a sensory cell in the brains of rainbow trout – close relatives of Pacific salmon, which return every year to their home rivers across 2,000 miles of open ocean to spawn – that acts as a magnetic compass.

Professor Michael Winklhofer, together with his team at Ludwig Maximilians University in Munich, found the cells in the part of the brain responsible for the fishes’ sense of smell. The cells contain iron oxide magnetite, which is magnetic. This magnetic substance is made by the fish themselves, though the exact process remains unknown.

The magnetism of the cells means they can pick up information from the earth’s magnetic field and convert this into a nervous impulse, helping to point the animal in the right direction.

Very few cells have this magnetic property. The scientists estimate only one in 10,000 have it.

The Munich team was able to isolate whole cells containing high levels of iron oxide magnetite from the tissue of rainbow trout and prove they are magnetic. Using a magnetic field, these scientists were able to demonstrate that the cells rotated while the non-magnetic cells remained still.

This finding reinforces the belief that large overhead electric pylons and undersea cables disrupt the magnetic field reception for many animals relying on their magnetic “compass” sense to get around.

Humans today do not appear to have these magnetic cells. It is possible however, that previous versions of humans did.